Modern microprocessors operate on relatively large words. For example, it is conventional for some microprocessors to process 64-bit words. As processor clock rates increase ever higher, the routing of such relatively wide-bit words on wide-bit buses becomes problematic. At high transmission speeds, the inevitable skew with regard to propagation on separate traces in the wide-bit buses may lead to unacceptable bit error rates. Moreover, such buses demand a lot of power and are expensive to design.
To enable the high-speed transmission of data words without the skew and distortion issues associated with high-speed wide-bit buses, serializer-deserializer (SERDES) systems have been developed. A SERDES transmitter serializes the data words into a high-speed serial data stream. A corresponding SERDES receiver receives the high-speed serial data stream and deserializes it back into the parallel data words. The serial transmission is usually differential and includes an embedded clock. The skew and distortion issues associated with high-speed wide-bit data buses are thus abated.
Although SERDES systems enable very high-speed data transmission such as 10 gigabits per second or even higher rates, the transmission characteristics for the differential serial data channel between the transmitter and receiver are not linear across the corresponding Nyquist channel bandwidth of 5 Ghz. Instead, the channel has a frequency-dependent response that reduces the amplitude of the higher-frequency portions of the data. To counter the resulting distortion, the SERDES transmitter includes an amplifier having a frequency response that is not linear across the channel bandwidth but instead emphasizes the higher frequency bands for the transmitted data spectrum. This emphasis can be problematic, however, in that it requires excessive amounts of power. But conventional attempts to reduce the transmitter power consumption limit the achievable bandwidth.
Accordingly, there is a need in the art for wideband and low-power transmitters that can compensate for channel frequency-dependent losses.